North American Birds

VOLUME 69 No1 2016

A Quarterly Journal of Ornithological Record Published by the American Birding Association. The mission of the journal is to provide a complete overview of the changing panorama of our continent’s birdlife.

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20a 20b 20c 20d c d d c d c 31 V O L U M E 6 9 ( 2 0 1 5 ) • N U M B E R 1 T H E M E N D O C I N O S H R I K E consisted of open, grazed, and drought-strick- en marine-terrace habitats with scattered low scrub, which might be favored more by Turke - stan than by Brown Shrike. However, given the infuence of Red-backed Shrike, which ap - pears to occupy habitats somewhat intermedi- ate to those of Brown and Turkestan Shrikes (Cramp and Perrins 1993), and unknown habitat usage when the Mendocino shrike was not at the mouth of Alder Creek (a majority of the time searchers were present), we believe that habitat selection is of little value in the shrike's identifcation. The Mendocino shrike was heard singing on several dates, and the song was recorded on 4 April 2015 by Steve Hampton and ar - chived at xeno-canto (www.xeno-canto.org; accessions XC234213, XC234214, under "identity unknown"). We have labelled these vocalizations as an "advertising song" (Cramp and Perrins 1993) given by male Lanius shrikes, which typically involves extensive mimicry learned from other species on either the breeding or winter grounds. The song of the Mendocino shrike consisted of a long string of quiet warbling musical notes, recall - ing to Moores those of Acrocephalus or Sylvia warblers, interspersed with occasional soft chatter as is typical of the genus. The advertising songs of Red-backed, Turke- stan, and Isabelline Shrikes as well as their hy- brids are reported to be quite similar, all av- eraging softer and more musical than the ad- vertising songs of Brown Shrike taxa (Cramp and Perrins 1993, Harris and Franklin 2000, Panov et al. 2011, Wassink 2015). At least in Korea, Brown Shrike taxa often include quite harsh phrases that recall vocalizations given by Thick-billed Warbler (Arundinax aedon) and Siberian Rubythroat (Calliope calliope), species that share a similar habitat and range with breeding Brown Shrikes (Moores, pers. obs. and audio recordings). However, com - parisons between each of these taxa are hin- dered by individual variation in these songs, in large part owing to extensive mimicry. Al - though we believe that this vocal evidence is at least consistent with the Mendocino shrike involving Turkestan as opposed to nominate cristatus or other Brown Shrikes, more detailed spectrographic analyses of the recordings as compared to those of other vocal studies (see Panov et al. 2011) may refne this assessment. The call notes of these shrikes are reported to differ more diagnostically than the songs (Cramp and Perrins 1993, Harris and Franklin 2000, Panov et al. 2011), but we have no de - scriptions or recordings of call notes given by the Mendocino shrike. Figure 20. Presumed Red-backed x Brown Shrike hybrids photographed at Perlis, Malaysia 28 February 2015 (a; Mun 2015) and 21 February 2015 (c) and in Kanagawa Prefecuture, Japan 27 February 2013 (b) and 21 April 2013 (d). Although resembling the Mendocino shrike in many respects, note a lack of whitish in the supercilial region, brownish uppertail coverts, similar in color to the back, brown or brownish-tinged rather than rufous bases in the formative rectrices, and more extensive and deeper buf tones in the sides and fanks. Note, however, white extend- ing beyond the primary coverts in the hybrid from Japan (b, d), a plumage feature only occasionally shown by Red- backed and rarely by cristatus Brown Shrikes (see text). The tail morphology of these hybrids (c, d) difers rather substantially from that of the Mendocino Shrike (Figure 15b, c) and would be expected of a Red-backed x Brown Shrike hybrid (Table 1b); the ratio c/d was calculated as 0.230 (image c) and 0.258 (image d). The Malaysian bird (a, c) was as an adult that had yet to replace its formative or basic outer rectrix when photographed on 21 February (c); this rectrix had dropped by 28 February (a). Photographs by Choy Wai Mun (a), Shinichiro Ueno (b), Piyapong Chotipuntu (c), and Yoshiki Watabe (d). Migration trajectories and vagrancy Early concerns about the identifcation of the Mendocino shrike as a Red-backed x Turkestan Shrike hybrid included the unlikelihood that a bird from a population breeding in interior southwestern Asia would occur in California. But we propose that such a vagrant occurrence is possible given the migratory pathways that such a hybrid would take between this breed - ing area and wintering areas in Africa (Figure 4), and given 180º misorientation (reverse mi - gration) theory that has been proposed for sev- eral other highly migratory, central Eurasian shorebirds and passerines reaching California and North America (Abbott et al. 2001, How - ell et al. 2014). Vagrants misorienting in an approximately 180º opposite direction from normal migratory paths may proceed over far-northern regions on a great-circle route to reach North America and may have an intrin - sic clock resulting in approximately the same distance of fight as would be found in normal migrants of the species. Applying 180º misorientation theory based on the southwestern and northeastern ends of the hybridization zone between Red-backed and Turkestan Shrikes (Figure 4) results in a pathway that includes the Pacifc North American coast, including Mendocino County and adjacent offshore waters (Figure 17a). The distance traveled to reach Mendocino County (9000 km) would be at the higher end of the usual migratory distance for such a hybrid (6000-9000 km). However, we believe that in this case the shrike may have found

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